KofanovV. A. “Massiveness of the Sets of Extremal Functions in Some Problems in Approximation Theory”. Ukrains’kyi Matematychnyi Zhurnal 45, no. 10 (October 25, 1993): 1356–1361. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5940.